Internal combustion engines have been used for many years for providing motive power for driving a vehicle. Most vehicles on the road today are provided with either a four, six, or eight cylinder engine which is selected based upon the typical torque demand requirements for the individual type vehicle being designed. For example, four cylinder engines are typically used for commuter vehicles which are compact and typically have low load requirements and limited performance expectations. Six cylinder and eight cylinder engines are typically employed in larger vehicles wherein larger load carrying capacity and higher performance are expected. Some of the existing vehicle designs have suffered from low fuel efficiency due to the fact that the internal combustion engine for the vehicle has to be designed with a sufficient capacity to meet the high torque demands that are only occasionally required.
Dual crankshaft engines overcome these deficiencies by providing a power train system that includes a dual crankshaft engine system with one of the engine portions being independently operable for providing driving torque to a transmission while the second engine portion can be utilized to supplement the driving torque of the first engine portion to meet higher torque demand requirements. These engine portions may be on one engine block or as separate engines. Operation of the dual crankshaft engine system is provided such that during normal driving at constant speeds and typical driving loads, the first engine portion is utilized for providing driving torque to the wheels of the vehicle. During periods of operation where increased levels of torque are required, such as during acceleration, pulling a heavy load, or climbing a hill, the second engine portion is operated in conjunction with the first engine portion for meeting the higher torque demand requirements.
A typical exhaust system for a single engine has a catalytic converter mounted along an exhaust pipe for cleaning the exhaust gases from the engine portion. Typically, catalytic converters operate efficiently at elevated temperatures. However, for a dual crankshaft engine system, since only one engine portion is operating in most driving circumstances, it can be difficult to keep a catalytic converter for the non-operating engine portion at an elevated temperature where it is most effective. Moreover, each catalytic converter must be sized according to which engine portions are in use with a given catalytic converter.